Film loop control for motion picture machines



June 30, 1936- P. J. BERGGREN I 2,045,748

FILM LOOP CONTROL FOR MOTION PICTURE MACHINES Original Filed Dec. 20, 1925 l :ii-53% Per Johan Berggren. y

INVENTOR.

E 7 A TTORNEY' Patented June 30, l1936 PICTURE l PATENT OFFICE A v aoisxus FILM Loor comm. Foa Mo'rIoN `MACHINES rer Johan Berggren-,New York, N. ,'Y.

Original application December 20, 1928, Serial No. 327,200. Divided and this application May 5, 1933, Serial No. 669,518. `Renewed December This invention relates to motion picture apparatus and with particularity. to methods and means for controlling the feeding movement of a motion picture fllmgthrough a projector. An object of the invention is to provide methods and means which are simple and efficient for supporting and retaining' a motion picture film steadily and stationarily in position opposite the l projection aperture while the pictures are being projected therethrough.

A further object of the'invention is toprovide means to prevent breakage or injury to the lm due to the jerking or snapping'action exertedthereon by the intermittent lm feeding mechanism.

A further object is to provide a pneumatic-.or

other form of compressible support for the upper loop of thevlm to maintain a yieldable tension therein ,acting in opposition to the intermittent feed mechanism.

A feature of the invention relates to the novel organization and arrangement of .elements which go to make up an economical and eiilcent film feeding mechanism for motion picture projectors.

The invention consists substantially in the construction, combination, location and relative organization of parts, all as willbe more fully hereinafter set forth as illustrated in the accompanying drawing, and nally pended claims.

Oth'erfeatures advantages of the invention not specifically enumerated willbe apparent after a consideration .of the following detail .descriptions and the appended claims.

Referring to the drawing: Figure 1 is a sectional view in elevation of a motion picture machine embodying the film 'threading and .holding loop sustaining means according to the invention;

Fig. 2 is a left hand end view in elevation `the structure of Figure 1. .Referring more particularly to Fig. 1 there is shown a portion of a motion picture projecting machine generally, off-known constructiorncom.- prising a lower film receiving or take-up reel |05. and an upper or film pay-off reel |054. Each of these reels is provided with asuitable enclosing casing` H3 and is attached respectively to the bottom and top of the projector casing 12.

filmA from the pay-o reel |05a. is threaded through 'a slot in the top ofthe casing 12 and thence to' and around the upper sprockets 92 fwhich are .adapted to be driven-at a continuous rate of speed. The nlm after leaving the sprocket 92 is formed into an upper loop H4v and passes pointed out in the ap- (c1. ss-is) `to be driven in an intermittent manner.- After leaving the intermittent and drive sprocket |00 the film is formed into the lower loop and A passes thence around-the lower sprocket device 89 which is continuously rotated. After leaving the sprocket 80 the lrn passes throughs. slit in the bottom of the projector casing and is received on the receiving reel |05. By means of the drivixg mechanism disclosed in detail in application Serial No. 327,200, the upper-and lower-nlm feed devices 02 and 89 respectively are continuously driven to effectV a continuous feed of the nlm, while the intermittent feed device |00 is actuated intermittently to cause the portion of the film which extends between the upper and lower loops H4, I1 to be actuated step-by-step. This stepby-step feed causes the pictures on the film to be successively brought'into framed position with reference to the projection aperture where they are arrested and held stationary so that each picture during its period of rest will be thrown onto the screen. The upper and lower loops I Il and Il'l of course permit the step-by-step feed of y the intermittent portion of the nlm without inter- I ference -with the continuous feeding action of 25 the upper and lower feed devices 92 and .89. lIn accordance with well known practice the feeding action of the several devices 92, |00, 89 is effected by the engagement of sprocket teeth in marginal holes formed in the lm tape. The above description sets forth the ordinary way in which a nlm tape is threaded through a motion picture projecting machine.V Due to the intermittent action of the sprocket |00 the same draws upon the surplus length of film afforded by'the upper loop and pays it out into the lower loop I1. Ordinarily the upper loop I l is formed in the lm at a-point between the delivery side of the upper continuous-feed sprocket 02 and the point whereA the lm enters the lm gate. Theoretically the upper loop bows upwardly inv a uniform curve as said loop is being formed by the feeding action of the upper sprocket device l, during .the time a. picture is projected onto the screen, that is during the time the portion of the lm which occupies they gate remains stationary. 4 Theoretically, also', the. action of the intermittent feed device |00, should cause a uniform shortening of the radius of the loop when said intermittent feed device is in operation land draws upon this loop. 'I'his ideal or theoretical action is' never attained in practice. On the contrary, in actual practice withfapparatus heretofore -employed the loopforms itself into -an elongated irregular shaped curve, building up a sharpened 55' "'ienif at which point the film frequently breaks in two when the stress of the sharp `snapping action of intermittent feed device isr imposed thereon. This snapping action is in the nature of a sharp whip likejerk or snap. Evenifthe 00 to move or shift the nlm or cause it to jump,

thereby varying orA altering its distance of the picture from the lens and hence altering itsv focus. 'I'his also tends to cause a jump or unsteadiness in the picture through both vertical and lateral or sidewise movement. This causes a most un- V desirable iiicker or movement of the. projected picture on the screen. A great deal of eiort and ingenuity have been 'expended in the endeavor to overcome and eliminate this most serious difculty, but, so far as I am aware these efforts have not resulted in a'successful solution of the problem. In accordance with my present invention I have provided a yielding support for the upper loop in the nlm which permits the loop to retain its eiilcient regularly curved contour, while at the same time being uniformly yieldable under the influence of the action of intermittent feed device. By providing an elastic yieldable support for .the loop, the said'loop is maintained under a degree of tautness, while being acted upon by the intermittent feed, which prevents the snapping or whipping action of the latter thereon, thereby avoiding breakage of the lm and preventing the reaction referred to, and the resultant unsteadiness, movement and loss of focal distance. In carrying out this idea of an elastic yieldable loop support it is important to avoid the use of anything which would mar or injure the iilm surface when applied thereto. I propose to employ for this purpose a comle medium. such, for instance as a body of air which I have found to.be one practical medium for the purpose. In carrying out my invention in one practical embodiment thereof, I deliver one or more jests of the compressible medium air, for example, and preferably at a point within the loop 4at approximately the midwidth of the film.

I have found excellent results in this respect are secured by enclosing the loop within a chamber formed by side walls but with an opentop.

In the drawing the walls of the chamber or enclosure are indicated at Ill, and the air jet at Il l, the air or other medium being Supplied t0 the jet bypipe connections |42, from any suitable source, as for example, and in the unitary self contained organized apparatus hereinbefore' described, Afrom the air compressor il. The film width itself constitutes the top closure for the chamber, and the transverse width of the film is such as to enable the lm to feed-through without frictional contact of its `edges with the inner surface ofthe side walls of thegchamber. By this arrangement the air body delivered under pressure from the jet spreads transversely across the iilm within the loop thereby affording an eiilcientA cushion support for the film its entiretransversewidth. It isI important to' avoid hack pressure, and henceI utilize the nlm width itself to constitute the top closure or dome for the chamber. The action is'two-fold. 'I'he velocity of the air delivered from the jet will act as a one point support for the nlm while the enclosed chamber makes possible the utilization of the air volume itselfasaicushioning medium throughout the whole inner surface ofthe loop. By reason of the elastic and yieldable nature of this support the intermittent feed actionis allowed to function without, causing any whipping or mapping of the loop, and'hence the'portion up tending tov prevent distortion of the loop, as

well as the production of anyf laterally waving 'motion Moreover, injury to the surface of the lm is also entirely avoided since there is nothing except the air now to come in contact therewith.

In connection with the use of an air liet as an elastic and yieldable cushion support for the upper loop of the film, I have also shown an air jet |43, for delivering a jet of air under pressure against the film while in the gate in order to pref vent any movement of the illm while the pictures thereon are being projected on to the screen. I do not claim thisnfeature, however, as it does no form part of my invention.

While one specific mannerof applying the air cushion to sustain the loop is disclosed in the drawing, it will be understood that the invention is not limited thereto. Furthermore, if desired an air cushion may be applied to the lower loop Ill as well, although this is not absolutely necessary. Furthermore, while an air cushion has been disclosed for sustaining the loop, it will be understood that any other compressible medium exhibiting like properties may be employed.

Various other changes and modifications may be made without departing from the spirit and scope of the invention.

This application is a division of application Serial No. 327,200, filed December 20, 1928.-

What is claimed is:

1. In a motionV picture projecting apparatus includingcontinuously and intermittently operating, illm feeding devices, the nlm being formed into a free loop intermediate said devices, and means for delivering a compressible gaseous medium within said loop to form an elastic cushion support therefor. Y

2. A motion picture apparatus including continuously and intermittently acting nlm feeding devices, the illn'i being formed into'a free loop intermediate said devices in combination with means to deliver air under pressure into said loop to form a yielding cushion support for the latter.

3. In a motion picture apparatus continuously and intermittently acting lm feeding devices, the film being formed into. a free loop intermediate said devices, a casing having enclosing side walls within which said loop is formed and means to deliver air under pressure withinsaid loop to form a yieldable compressible support for said loop. 4. In a motion picture apparatus continuously and intermittently acting film feeding devices. the illm being formed into a free loop intermediate said devices, a casing having enclosing side vwalls within which said loop is formed and means PERJOHAN BERGGREN. 

